This book constitutes the proceedings of the 19th International Symposium on Acoustical Imaging at the Ruhr-University Bochum, Germany during April 3 -5, 1991. It was the first time that the symposium was held in Europe after major political changes happened in that area. The freedom to travel for all people from eastern European countries was an obvious reason for the great numbers of sub- mitted abstracts and for numerous conference participants. 193 of 239 submitted contributions from 29 countries were accepted for presentation by authors from USA (13%), Canada (2%), Japan (7%), Peoples...